For the president, next week is being billed as the official launch of his re-election campaign. Mr. Obama will be holding rallies in the swing states of Ohio and Virginia. But it would be hard to tell a difference from this week, when Mr. Obama made a tour of college campuses in three other battleground states.

NPR's Scott Horsley reports on what might be called the overture to the 2012 contest.

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SCOTT HORSLEY, BYLINE: This week's trip was a kind of tune-up for the fall campaign. Like the Hawkeye Marching Band that opened for him yesterday at the University of Iowa, the president is easing his way into general election mode - practicing the scales you'll be hearing a lot more of between now and November.

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HORSLEY: Mr. Obama showed he can still fill a basketball arena. Speaking to thousands of supporters in Iowa, Colorado, and North Carolina, he delivered a variation on the theme he introduced last year in Osawatomie, Kansas: attacking the rise of income inequality and defending a strong middle class.

PRESIDENT BARACK OBAMA: I don't want this to be a country where a shrinking number of people are doing really, really well, and then a growing number are barely able to get by. I don't want that future for you. I don't want it for my daughters. I don't want it for America.

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HORSLEY: The official business on this trip was a call for Congress to preserve low-cost student loans. But that's just one small illustration of the president's larger campaign theme that we're all in this together. And that Americans -especially those who are most successful - have an obligation to everyone else.

OBAMA: You, me, all of us, we're here because somebody somewhere - starting with our parents or our grandparents or our great-grandparents, they made an investment not just in themselves but in each other and in the future of our country. And now it's our turn. It's our turn to keep that promise alive.

HORSLEY: Roberta Aragon is still inspired by that message, just as she was four years ago.

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ROBERTA ARAGON: That was the first time I ever voted was for him. So he made me change my mind. I'll be a voter for the rest of my life, because I think it does make a difference, somebody that actually cares for the American people - not like red, blue. It's about American people.

HORSLEY: But polls suggest many young people are not as enthusiastic as they were last time. Their impatience with the slow economic recovery was reflected in Andrew Speck's impatience, as he waited for the president to speak.

ANDREW SPECK: Just kind of curious. I don't know though now, I mean it's been two hours and nothing's happened. So not that good.

HORSLEY: You know, the president's in campaign mode when he makes a seemingly impromptu visit to a local restaurant - camera crews in tow.

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HORSLEY: In Colorado this week, Mr. Obama stopped by a burger and pizza joint called The Sink, that's popular with university students. Business major Elaine Fairbanks pitched him on her idea for a cheese fry restaurant. It sounds good, the president said. It sounds low calorie, also.

ELAINE FAIRBANKS: I have lots of great ideas. But that's the first thing I could think of.

HORSLEY: Fairbanks called the encounter awesome, but nerve-wracking.

Outside the restaurant, there were more nerves on display, when a woman named Kolbi Zerbest spilled what appeared to be yogurt on the president's trousers.

OBAMA: More hazardously, she spilled yogurt on the Secret Service, which you just...

HORSLEY: The president quickly dried off his pants. Zerbest wound up on "The Today Show." That's how it goes on the campaign trail. One minute, you're wowing fans with your vision of a strong, inclusive economy. The next, you're scrubbing a smoothie off your pants. If you want to be president, you've got to roll with it.